Viral inclusions in monocotyledons infected by maize streak and related geminiviruses

Abstract

Isolates of maize streak virus (MSV) were examined by thin-section electron microscopy in plants, assessed for characteristic features of infection and compared with other related geminiviruses infecting monocotyledons from Africa, islands in the Indian Ocean, and the Pacific Island of Vanuatu. Arrays of virus particles, often crystalline, were most often seen in the nucleus. The morphology of the nuclear crystalline arrays was characteristic of certain isolates or groups of isolates (strains). Infected nuclei could be seen in cells from the phloem parenchyma, vascular bundle sheath and mesophyll tissue, and also in epidermal guard cells of plants infected with the maize strain of MSV. The particle arrays varied in morphology from regular rows of virions forming distinctive blocks, to randomly arranged aggregates in certain areas of the nucleus. We consistently failed to find viral crystalline arrays associated with infection of panicum streak virus (PSV) and sugar cane streak virus (SSV) isolates either in these hosts or in maize. Occasionally arrays of MSV particles were found outside the nuclear envelope in physiologically active cells. Accumulations or sheets of MSV particles were seen lining the walls ofsome phloem companion cells. Crystalline aggregates of particles were frequently observed in the cell vacuole. after lysis of the nuclear membrane of dead cells which made up the chlorotic lesions, the typical symptom of virus infection. Virus preparations from all hosts contained typical geminate particles regardless ofthe morphology ofthe virion arrays. The effect on chloroplasts appeared to vary between isolates and this is discussed in relation to lesion colour. The arrangement of virions in the nucleus as a taxonomic character is diagnostic for MSV. Inclusions with crystalline structure found in sieve elements of infected plants were not immunogold labelled when thin sections were probed using antiserum to the virus particles.

Replicative intermediates of maize streak virus found during leaf development

“…At least for the mature cells in leaf lamina tips, it is conceivable that the most important fate of RCR products is encapsidation. These virions then accumulate to form paracrystalline inclusions within infected cell nuclei that may be taken up by leafhopper vectors (Pinner et al, 1993). The late accumulation of RCR intermediates therefore fits well with the ultrastructurally observed accumulation of MSV virions in older maize tissues (Pinner et al, 1993).…”

“…Starting with all replication modes in the shoot apex, MSV RCR increases in prominence during the differentiation of infected cells. Given that monomeric ssDNA molecules are both the products of RCR and the encapsidated MSV genomes that accumulate within infected tissues in preparation for transmission (Lucy et al, 1996;Pinner et al, 1993), this time course makes good biological sense.…”

The nuclear reticulum in placental cells ofLilium regale is a part of the endomembrane system

“…However, nuclear vacuoles are quite distinct from the nuclear reticulum in their structure as well as in their presumed function. Various nuclear inclusions can also result from pathological infections (Hong et al 1997, Gilberet and Gosh 1993, Kanyari 1996, Pinner et al 1993, Koning et al 1993, Maeno et al 1993). Viral infections in plants (Gao andNassuth 1993, Pinner et al 1993) can cause nuclear alterations and changes in some cytoplasmic organelles like mitochondria and chloroplasts.…”

Virion Stability Is Important for the Circulative Transmission of Tomato Yellow Leaf Curl Sardinia Virus by Bemisia tabaci , but Virion Access to Salivary Glands Does Not Guarantee Transmissibility

“…The anti-TYLCV (As-588) and anti-ACMV (As-421) polyclonal sera (gift of S. Winter, DSMZ, Braunschweig, Germany) were cross-absorbed with healthy plant extracts or with combined healthy plant and insect tissue extracts, respectively. For immunogold labeling, ultrathin sections (ϳ70 nm) of plant and insect tissue that were mounted on carbon-coated gold grids as described previously (62) were incubated overnight at 4°C in the above sera, diluted 1:200 in blocking buffer (200 mM Tris-HCl [pH 7.4], 1% Tween 20, 1% bovine serum albumin, and 0.1% gelatin). Grids were washed for 1 min in distilled water and incubated for 1 h at room temperature in goat anti-rabbit immunoglobulin G serum, conjugated to 15-nm gold particles (1:20 dilution) (Janssen AuroProbe; Janssen Pharmaceuticals, NJ).…”